The present invention relates to a method of manufacturing an organic electroluminescent (EL) element, an organic EL element, and an organic EL display device.
An organic EL element is an element which has a configuration in which a thin film containing a fluorescent organic compound is held between a cathode and an anode. In the organic EL element, electrons and holes are injected from the respective electrodes into the thin film to generate excitons through the recombination of the electrons and holes. The organic EL element produces luminescence by utilizing emission of light (fluorescence or phosphorescence) at the deactivation of the excitons.
The features of the organic EL element is that it is possible to obtain a high intensity surface luminescence on the order of 100 to 100,000 cd/m2 at a low voltage of less than 10V, and that it is possible to produce luminescence of from blue to red y the selection of the kind of fluorescent material.
The organic EL element is drawing attraction as a device for realizing a large area full color display element at a low cost (see, Institute of Electronics, Information and Communication Engineers (IEICE) Technical Report, Vol. 89, No. 106, 1989, p. 49). According to the report, bright luminescence of blue, green and red were obtained by forming a luminescent layer using an organic luminescent material which emits strong fluorescence. This fact is considered to mean that it is possible to realize a high brightness full color display by using an organic coloring matter which emits strong fluorescence in a thin film state and has less pin hole defects.
In addition, in Japanese Laid-Open Publication No. Hei 5-78655, there is proposed to use an organic luminescent layer containing a luminescent material which is formed of a mixture of an organic charging material and an organic luminescent material, thereby obtaining a high brightness full color element by preventing quenching due to higher concentration as well as expanding the latitude in the selection of the luminescent material.
Further, in App. Phys. Lett. Vol. 64, 1994, p. 815, it is reported that a white luminescence was obtained by using polyvinyl carbazole (PVK) as a luminescent material and doping it with coloring matters corresponding to three primary colors R, G and B. However, in neither of the above references, the configuration or the method of manufacture of an actual full color display panel is not shown.
In the organic thin film EL elements using the organic luminescent materials described above, in order to realize a full color display device, it is necessary to arrange organic luminescent layers which emit any one of the three primary colors for the respective pixels. However, there is a problem in that a polymer or precursor that forms the organic luminescent layer lacks a sufficient resistance to a patterning process such as photolithography, so that it is very difficult to carry out patterning with highly precision.
Further, when several organic layers are to be formed by a vacuum deposition method, it takes a long time. Therefore, such a method cannot be said to be an efficient method of manufacturing the element.
It is an object of the present invention to provide a method of manufacturing an organic EL element which makes it possible to carry out patterning easily and precisely, can attain optimization of a film design in a simple manner, and has excellent luminescence characteristics, as well as to provide an organic EL element and an organic EL display device.
In order to achieve the above object, the manufacturing method of an organic EL element according to the present invention comprises the steps of forming pixel electrodes on a transparent substrate, forming on the pixel electrodes by patterning at least one luminescent layer having a certain color and made of an organic compound, and forming a counter electrode opposing the pixel electrodes, wherein the formation of the luminescent layers is performed by means of an ink-jet method.
In the present invention, it is preferable that the organic compound is a polymer organic compound. In this case, it is preferable that the polymer organic compound is a hole injection and transfer type material. Preferably, such a polymer organic compound is a polyparaphenylene vinylene or its derivative or a copolymer which contains at least either one of these compounds.
In this connection, when an organic luminescent material itself is not a hole injection and transfer type material, as is the case in the above-mentioned polymer organic compound, it is possible to add a hole injection and transfer type material to the luminescent layer in addition to the luminescent material.
Further, it is also preferred that the at least one luminescent layer comprises three layers having different colors, in which the at least two colors out of the luminescent layers of three colors are patterned by means of an ink-jet method. The three colors are red, green and blue, and it is preferable that the red luminescent layer and the green luminescent layer are patterned by means of an ink-jet method. In this case, it is more preferable that the blue luminescent layer is formed by a vacuum deposition method. Further, it is preferable that the blue luminescent layer is made of an electron injection and transfer type material, such as an aluminum quinolinol complex.
In the manufacturing method for the organic EL element according to the present invention, it is preferable that at least one luminescent layer is laminated with a hole injection and transfer layer, and it is also preferable that a protective film is formed on the counter electrode.
In the manufacturing method for the organic EL element of the present invention, it is preferable that the transparent substrate is provided with thin film transistors for driving respective pixels.
Further, it is preferable that the pixel electrodes are formed into a transparent pixel electrode.
Furthermore, the organic EL element of the present invention is provided with a transparent substrate, pixel electrodes formed on the transparent substrate, at least one luminescent layers having a certain color and made of an organic compound, the luminescent layer being patterned on the pixel electrodes by an ink-jet method, and a counter electrode formed on the luminescent layer.
It is preferable that the organic compound is a polymer organic compound, and it is more preferable that the polymer organic compound is a hole injection and transfer type material.
Moreover, it is preferable that the polymer organic compound is a polyparaphenylene vinylene or its derivative or a copolymer containing at least one of them.
It is preferred that the at least luminescent layer includes three layers having different three colors, and it is preferable that two layers thereof in the luminescent layers of three colors are patterned by an ink-jet method. The three colors are red, green and blue, and it is more preferable that the red luminescent layer and the green luminescent layer are separately patterned by an ink-jet method. In this case, it is more preferable that the blue luminescent layer is formed by a vacuum deposition method.
It is preferable that the blue luminescent layer is made of an electron injection and transfer material. As for such a blue luminescent layer, a layer containing an aluminum quinolynol complex can be mentioned.
Moreover, it is preferable that at least one luminescent layer is laminated with a hole injection and transfer type layer, and it is more preferable that a protective film is formed on the cathode.
Furthermore, it is preferable that the pixel electrodes are formed into a transparent pixel electrode.
Moreover, the organic EL display device according to the present invention is characterized in that it includes the organic EL element described in the above.